Decide which instant messaging client to use for the new messaging bundle

Description

We need to decide which client we would use for the new bundle. We analyzed three options:​Pidgin/libpurple, ​xmpp-client, and ​Instantbird. We picked Instantbird because even though it lacks Off-the-Record support (which we will work on), it meets all the other goals, including having a clean user interface, good protocol support, pure JavaScript implementations, cross-platform bundles, support for multiple languages and also the fact that we can use the in-house Mozilla expertise. That concludes this task.